@act Usually I would be inclined to agree with you - that anything is possible (or at least that frame of mind can inspire innovation and help overcome daunting challenges). An M4/3 to M4/3 SpeedBooster may not be 'impossible', but as Brian pointed out (and he is the optical engineer for the SpeedBooster): it's not really technically feasible without being prohibitively ineffective. I'm inclined to take his word for it, as the Metabones SpeedBooster has set the bar for quality focal reducers.

To answer your other point - have you ever used an FD to EOS or Minolta to EOS adapter with corrective elements? In my experience they absolutely destroy the image sharpness, introduce other visual artifacts, reduce light transmission and tele-extend focal length (which, I believe, are the points Brian was getting at when he said 'you would have to sacrifice so much image quality that the device would effectively be useless').

And to be fair, focal reducers have been around for AGES in cinema for PL mount and in astral photography for camera-telescope adapters. They just hadn't been introduced for public consumption until recently.

Don't get me wrong, I love to dream, but unfortunately some dreams are just for the pillow.

@CFreak Sure, for example: the Hawk and/or Vantage 0.7x focal reducer (which was originally designed for the Hawk 150-450mm/T2.8 around 12 years ago). It's no surprise you haven't come across one, they aren't common. They cost an arm and a leg and are only usable on some telephoto and periscope lenses, but there you have it. I guess 'AGES' is a subjective term, but 2002 is a long time ago for a quickly evolving industry. Of course there are other reducers out there for c-mount, etc that have been around longer (for astral stuff), and there MAY be even older cinema focal reducers out there, now buried, but the Hawk is relatively easy to look up.

@JuMo: Yes, I never worked with Hawk lenses. That explains it. The last Anamorphic movie I worked on was in 2000. In my Camera Assistant career I worked with Panavision anamorphics (C, E and Primo series) and Arri's Arriscope series. No Hawks. Here's the link: http://www.vantagefilm.com/en/news/news_2002-08_01.shtml Although I doubt that product was intended for use on anamorphics, I see they also have spherical lenses. For some reason I associate Hawk with anamorphic. Must have been all the advertising. Must be hard for a German lens company to get noticed when up against Zeiss, Leica, Schneider all from the same country.

What would truly be amazing (perhaps someone already addressed it in the last 27 pages), is if the speedbooster could be some sort of Adapt-all mount. One side would be m43, the other side could have snap on adapters to make it the appropriate size for FD, Nikon, EOS, etc. That way the expensive part of the adapter (the glass) would only need to be purchased ONCE.

I'm sitting here thinking "man, I wish I could get an Nikon to FD mount ring, then I could just get the FD speedbooster and be good to go". But as already pointed out, no such adapter exists that we know of. So multiple Speedboosters would be necessary, and that's just way out of my budget.

@JuMo Thanks for your answer! ;) Someone else know the behaviour of the Speedbooster aperture ring? "F" on the speedbooster is f1.8 on the Sigma 18-35 lens, so "1" on the speedbooster is...?? Thank you. ;)

Small, handheld clip with GH3 with Minolta Rokkor PG 58mm/f1.2 + Metabones Speed Boster which makes it 41mm/f0.85. Clip was deshaken but without cropping.

I'm sure someone's asked about this, or suggested this, but... well, I'm wondering if the ability to use Nikon lenses on MFT cameras gives us a huge price break in the long run. Buying MFT lenses can be expensive... but there are a lot of Nikon lenses out there being sold through Ebay and used-equipment sources. Has anyone 'run the numbers" on the choice of buying MFT lenses in the future, or buying a Speed Booster and using quality Nikon lenses from here on in?

@JuMo I've been looking at the SLR Magic 12mm lens, which is pretty wonderful, and it's a mechanical focus so it'll work well with my follow-focus rig. That's something legacy lenses offer-- mechanical focus, and not that ersatz manual system on motorized MFT lenses.

But the SLR Magic lens is what, six hundred dollars? I figure, if the Metabones is four hundred, and if a wide manual-focus lens from Nikon (or Canon or Zeiss) is available for under two...

For a wide on my FD set I like the 20mm f2.8 @ f4 (SB brightness equiv to f2.8) to reduce the slight bloom - or occasionally f5.6 for even a little sharper image. 20mm is the equivalent FOV of a 14mm, which might not be wide enough for everyone on the BMPCC, but I've been enjoying it. I haven't tried the FD 17mm f4 yet, but that would give you a 12mm equivalent FOV, which, at the wide end, those extra 2mm make a difference.

Speed Booster aside, the c-mount 10mm f1.6 Kern covers the sensor well and is rectilinear. It's tiny, like a lot of c-mounts it looks kind of comical, but it's actually quite a nice little lens (if you find a good copy).

@ahbleza That shot just kills! I want to see the film based on this still alone!

@Brian_Siano if your question was meant as the best value for your money, you're ceirtanly on safer side with good Nikkor glass. But you pay about at least double there than for other good vintage lenses. But if you sell Nikkors some day, you will have your $ any time back. For all other lenses: not as sure. You must know.

Nikkors fit not only on Metabones Speed Booster, but on so many other cameras and all Nikon cameras until today (even on Canon cameras)

@Baramed the original Nikon F/G version which was printed F-through-8 on the aperture ring had a non-linear behavior. The newer version, printed F-through-7 is almost perfectly linear, so each step should correspond to one stop.

It was released and is sold out at the moment – I'm waiting too…